1. Field of the Invention
The present invention relates to a system/method for efficiently calculating the optimal assembly tolerance of a three-dimensional mechanism assembly model.
2. Description of the Related Art
As is well known, tolerance defines how much deviation from a design reference value is allowed in the actual production of a product. Too much tolerance leads with high probability to a defective product. Too small a tolerance leads to both a heavy workload and a high cost since it requires high-accuracy production work. Therefore, it is important to set optimal tolerance. However, in many cases, a designer arbitrarily sets tolerance based on his experience and sense of an actual job. Therefore, a system for supporting a designer in efficiently setting optimal tolerance is required.
Conventional tolerance analysis systems are, for example, as follows.
(1) J. Lee and G. E. Johnson, xe2x80x9cOptimal Tolerance Allotment Using a Genetic Algorithm and Truncated Monte Carlo Simulationxe2x80x9d, Computer-Aided Design, Vol. 25, No. 9, pp.601-611 (1993).
(2) Victor J. Skowronski and Joshua U. Turner, xe2x80x9cEstimating Gradients for Statistical Tolerance Synthesisxe2x80x9d, Computer-Aided Design, Vol. 28, No. 12, pp.933-941 (1996).
(3) Victor J. Skowronski and Joshua U. Turner, xe2x80x9cUsing Monte-Carlo Variance Reduction in Statistical Tolerance Synthesisxe2x80x9d, Computer-aided Design, Vol. 29, No. 12, pp.63-69 (1997).
(4) xe2x80x9cCE/TOL 6"sgr"xe2x80x9d manual, published by Rand Technologies Ltd.
(5) xe2x80x9cVALISYSxe2x80x9d manual, published by TECNOMATIX Ltd.
(6) C. M. Creveling, xe2x80x9cTolerance Designxe2x80x94A Handbook for Developing Optimal Specificationxe2x80x9d, Addison-Wesley (1997).
In the conventional tolerance analyzing system (for example, (4) or (5)), three-dimensional assembly tolerance could not be designated so that the play in a groove or the play of a shifting gear can be faithfully reproduced. Since both of the systems adopts a method for designating a tolerance in a specific position/orientation of a mechanism based on probability distribution, how the total assembly tolerance in the case where the mechanism causes three-dimensional dynamic drive is distributed cannot be analyzed. Although in the papers (1), (2) and (3), a method for calculating tolerance distribution based on the Monte-Carlo method is discussed, both of the methods is limited to two dimensions and is limited to the analysis of one specific static position/orientation.
It is an object of the present invention to enable the efficient calculation of optimal assembly tolerance so as to meet the design specification value of a three-dimension mechanism assembly model and to provide an assembly tolerance analysis system and method thereof for supporting the judgment work of a user by calculating/presenting both sensitivity and assembly tolerance that will be close to optimal.
An assembly tolerance analysis apparatus according to the present invention analyzes assembly tolerance. The assembly tolerance analysis apparatus comprises an object shape/assembly information storage unit storing shape/assembly information of each part composing an analysis target, a Monte-Carlo population generation unit generating a population of assembly samples with a slightly different mounting position/orientation of each part using Monte-Carlo method based on an initial setting value of an assembly tolerance of each part composing an analysis target, a simulation unit simulating an operation of the analysis target in the part mounting position/orientation for each assembly sample obtained by the Monte-Carlo population generation unit using the shape/assembly information and calculating an operation locus of an arbitrary focus point, and an allowable tolerance range backward analysis unit selecting a locus located within a design specification range imposed on the focus point from a plurality of operation loci and determining a new assembly tolerance based on the mounting position/orientation of each part of an assembly sample corresponding to the selected locus.
According to the assembly tolerance analysis apparatus described above, since an assembly sample, in which the operation locus of a focus point is located within the design specification range, is selected from many assembly samples generated by the Monte-Carlo method, optimal assembly tolerance can be determined with high probability by using the mounting position/orientation data of each part obtained when this selected assembly sample is designated (for example, the minimum value or the maximum value of the data as the assembly tolerance).
The new assembly tolerance determined by the allowable tolerance backward analysis unit does not always guarantee that all the operation loci are located within the design specification range. Therefore, the process must be performed again from the beginning using the new assembly tolerance and it must be confirmed that all the operation loci are located within the design specification range. The process of the Monte-Carlo population unit or simulation unit requires a lot of processing time, particularly, if there are many assembly samples.
Therefore, for example, an assembly sample in which the mounting position/orientation of each part meets the new assembly tolerance can also be selected from the assembly samples, and it can also be judged whether all the operation loci corresponding to the selected assembly samples are located within the design specification range. Thus, there is no need for a user to wait during the process and, accordingly, the entire efficiency of the process can be improved.
The present invention is not limited to the assembly tolerance analysis apparatus described above, and the invention can also be incorporated into a storage medium that stores a program for enabling a computer to implement the functions of this assembly tolerance analysis apparatus, transmission signal thereof or method thereof.